This column will change your life: Are you an Asker or a Guesser?

The advice of etiquette experts on dealing with unwanted invitations, or overly demanding requests for favours, has always been the same: just say no. That may have been a useless mantra in the war on drugs, but in the war on relatives who want to stay for a fortnight, or colleagues trying to get you to do their work, the manners guru Emily Post's formulation – "I'm afraid that won't be possible" – remains the gold standard. Excuses merely invite negotiation. The comic retort has its place (Peter Cook: "Oh dear, I find I'm watching television that night"), and I'm fond of the tautological non-explanation ("I can't, because I'm unable to"). But these are variations on a theme: the best way to say no is to say no. Then shut up.

This terminology comes from a brilliant web posting by Andrea Donderi that's achieved minor cult status online. We are raised, the theory runs, in one of two cultures. In Ask culture, people grow up believing they can ask for anything – a favour, a pay rise– fully realising the answer may be no. In Guess culture, by contrast, you avoid "putting a request into words unless you're pretty sure the answer will be yes… A key skill is putting out delicate feelers. If you do this with enough subtlety, you won't have to make the request directly; you'll get an offer. Even then, the offer may be genuine or pro forma; it takes yet more skill and delicacy to discern whether you should accept."

Neither's "wrong", but when an Asker meets a Guesser, unpleasantness results. An Asker won't think it's rude to request two weeks in your spare room, but a Guess culture person will hear it as presumptuous and resent the agony involved in saying no. Your boss, asking for a project to be finished early, may be an overdemanding boor – or just an Asker, who's assuming you might decline. If you're a Guesser, you'll hear it as an expectation. This is a spectrum, not a dichotomy, and it explains cross-cultural awkwardnesses, too: Brits and Americans get discombobulated doing business in Japan, because it's a Guess culture, yet experience Russians as rude, because they're diehard Askers.

Self-help seeks to make us all Askers, training us to both ask and refuse with relish; the mediation expert William Ury recommends memorising "anchor phrases" such as "that doesn't work for me". But Guessers can take solace in logic: in many social situations (though perhaps not at work) the very fact that you're receiving an anxiety-inducing request is proof the person asking is an Asker. He or she is half-expecting you'll say no, and has no inkling of the torture you're experiencing. So say no, and see what happens. Nothing will.